Pacemakers and implantable cardioverter/defibrillators (ICDs) have become useful treatment devices for those with cardiac dysfunction. These devices provide electrical stimulus that helps a patient's heart function properly. One aspect of such devices is the desire to accurately identify whether and when a patient is experiencing a malignant cardiac condition. However, the heart may experience not only normal sinus rhythms but also various forms of arrhythmias, such as atrial fibrillation, atrial tachycardias, ventricular fibrillation, and ventricular tachycardias. Not all of these arrhythmias are malignant. Because the application of cardioversion or defibrillation stimulus can be discomforting to a patient, unnecessary application of stimulus should be avoided. Further, erroneous application of stimulus can cause a patient's heart to enter a malignant cardiac condition such as fibrillation. Methods and devices that provide additional approaches to discriminating between malignant and non-malignant cardiac conditions are therefore desired.